Antenna system



Sept. 26, 1950 F. o. CHI-:sus ETAL 2,523,280

ANTENNA SYSTEM Filed Aug. 24, 1945 ,l

BY 7 /Af ATTORNEY Patented Sept. 26, 1950 UNITED STATES PATENT OFFICE ANTENNA SYSTEM Frank 0. Chesus, Jackson Heights, and Frank G.

Thomas, Islip, N. Y., assignors to Federal Telephone and Radio Corporation, New York, N. Y., a corporation of Delaware Application August 24, 1945, Serial No. 612,502

s claims. (c1. 25o-33.59)

This invention relates to antenna systems and particularly to directional arrays which may be used in direction iinders and the like.

In many antenna systems, particularly directional systems, it is desired that the iield pattern of the antennas be unaffected by radiation or elds emanating from the lead-ins, or connecting transmission lines, as well as from the supporting structure. For example, in the attempt to eliminate polarization errors from direction finders using antenna arrays, the transmission lines connecting the spaced antennas have been enclosed in metallic Sheaths to thereby shield the lines and isolate said lines from the antennas. However, horizontally polarized Waves induce voltages in the horizontally disposed sheaths which voltages have fields with vertical components, which vertical components affect the antennas and produce polarization errors.

An object of the present invention is the provision of an antenna system in which the antenna is substantially isolated from its transmission line, that is, from reradiation or a eld emanating from said transmission line.A

Another object of the present invention is the provision of an antenna array of the Adcock type having spaced apart antennas which are crossconnected by a transmission line cased in a metallic sheath and in Which the field emanating from voltages induced in such sheath by horizontally polarized Waves, will not substantially affect the vertical antennas, thus minimizing polarization errors.

Other and further objects of the present invention Will become apparent and the invention will be best understood from the following description of an embodiment thereof, reference being had to the drawings, in which:

Fig. 1 is a schematic perspective view of an antenna system embodying our invention, and a block diagram showing its relation to a direction nding receiver;

Fig. 2 is an enlarged schematic side elevational View of a pair of the antenna units and the connecting transmission line of Fig. 1.

Referring now to Fig. 1, four equally-spaced vertically-disposed antenna units I-li. respectively are mounted on cross-arms 5 and E supported at their centers by a mast 1. 6 are preferably made of insulating material. Antenna units I-ll form part of an Adcock array of the interconnecting vertical U type, with antenna units I and 3 forming one pair and antenna units 2 and II the other pair. Antenna units I and 3 are cross connected by a Shielded transmis- The cross-arms 5 andr 2 sion' line 8 and antenna units 2 and 4 connected by a shielded transmission line 9, each of said lines 8 and 9 being substantially in the form of a U, the sides of which are substantially vertical and the bottom portion of which is substantially horizontal.

Adjacent each of the antenna units there `is provided a set I0 of horizontally disposed circular plates or discs II, each set consisting of a plurality of spaced, horizontal, parallel discs. Each of said discs II is provided with a central opening I2 through which theA transmission line extends, the discs Il of each set being electrically conductively connected adjacent thelopenings rI2 to each other and to the outer shield' I3 of theV shielded transmission lines 8 or 9.' Each set, IU of discs is mounted adjacent one end of one of the transmission linesl 8 or 9 adjacent the antenna unit connected to said end. f

rIfhe middles of the U-shaped. shielded transmission lines 8 and 9 extend through a junction box I4 supported onmast 1, leads I5 from said junction box going to a goniometer I6 which in turn is connected through suitable leads I'I to a direction finding receiver I8 having in its output an indicator I9, which may be in the form of a cathode ray oscillograph or the like. v

While the specific antenna units employed may be monopoles, or dipoles of 'known construction,

we prefer to use the type of antenna unit described in our co-pending application, Serial No.

613,329, led August 29, 1945, now Patent No; 2,454,774, issued November 30, 1948.

Referring now to Fig. 2, antennaunitl will now be described, it being understood that thev other units are similar in construction. Anten na unit I consists of three cylindrical conductors coaXially arranged, the innermost one being 20, the intermediate one 2l and the outside conductor 22. AThe intermediate conductor 2l extends beyond conductors 20 and 22 and may be twice as long as they are.' The top of the innermost conductor 2l) is connected by a resistance 23 to factorily over a relatively wide band of frequencies.

Transmission line 8 which has two inner con-y` are CI'OSS 'sheathtoward the antenna units.

ductors 24 and 25 surrounded by a metallic sheath I3 has one of these inner conductors 25 connected to the bottom of innermost conductor of antenna unit I While the other inner conductor 24 of transmission line 8 is connected to the outer surface of the outside conductor 22 of antenna unit. l adjacent the lower end thereof. At its other end inner conductor 25 of transmission line 8 is also connected to the innermost conductor 20 of antenna unit 3 while transmission line 24 is likewise connected to the outer` surface of the outside conductor 22 of antenna unit 3.

The arrangement hereinabove described substantially minimizes polarization errors. 1`n part this is due to the fact that the horizontal portion of transmission line 8 and transmission line;

9 is disposed such a distance below the set I0 of discs that at said discs the eld produced by voltages induced in said horizontal portion is almost at right angles to the discs. The sets of discs serve to shield the antennas. from the effects of the horizontal polarization and from any currents' along the sheaths of said transmission line. According to our present understanding of the effects of said discs, there are several different Ways in which they serve to prevent the transfer of energy from the shield I3 of the transmission lines to the antenna units, in addition to their function as electrostatic shields.

The; discs may be considered as transmission lines shorted at their inner Yends and offering a very high limpedance to current passing from said Since these ,transmission lines are substantially less than a quarterwavelength, (the distance between any twoantenna units is a quarter wavelength or less and the discs have less diameter than this distance), these transmission lines look like an inductance and oifer high impedance to said currents. The effectv of the capacity between the lower end of the antenna units and the topmost disc ofthe sets I9 of discs, that is the amount of energy transferred' across said' capacity, depends upon the potentials present. y Looking at the arrangement fromthis aspect, the effect of the discs is like that of a mass at the end of a point reducing the potential of said point. There is also some type of transformer effect. produced by said disc arrangement which so affects. the potentials that there is very little transfer of energy from' the sheaths I3- to the antenna units I-4. The effect of the ,plates or discs in reducing the horizontal polarization errors is not fully understood and the theoretical considerations outlined above may not be all borne out. However, in actual practice it has been found that two or more discs arranged as described do reduce polarization errors to' a negligible value. Experience shows that three or four discs are suiiicient to substantially eliminate the polarization errors and that'additional discs above this number are not necessary. By use of our invention, performance of a portable direction nder is found to be substantially asgood as one in which thevertical U interconnecting leads are buried three or more feet under a good conductin ground of extensive. surface.

While We have described one. embodiment of our invention it will be apparent to those versed in the art that numerous changes may be made there-in without. departing from the teachings of our invention. For example while the antenna arrangement described is intended to be stationary, it is Vobvious that it may be made rotatable. DilTerent types of vertical antenna units may be employed instead of that type specically here described. Accordingly, while we have described above the principles of our invention in connection with specific apparatus, it is to be clearly understood that this description is made only by way of example and not as a limitation on the scope of our invention as dened in the accompanying claims.

We claim:

1. An antenna system comprising an antenna unit, a transmission line including a ,pair of conductors coupled at one end to said unit, a shield about said line, means insulating said antenna unit from said shield, and a plurality of spaced metallic plates of non-resonant length at the system Aoperating' `frequency each having an opening therein through which said line extends, said plates being positioned adjacent said antenna unit and conductively connected to said shield.

2. An antenna system according to claim 1 wherein said'plates are parallel to each other and transverse to the portion of the transmission line which they surround.

3. An antenna system according to claim l wherein said metallic plates are in the form of circular discs eachl having a central opening and said discs are conductively connected to the shield of the line adjacent the opening and effectively prevent the transfer of radiant energy from said shield to said unit.

4. An antenna system according to claim 1 wherein said antenna unit is elongated and extends in a given direction, said plates extend in planes transverse to said given direction, and the portion of said transmission line surrounded by said .plates extends substantially in a line with said given direction.

5. An antenna system according to claim 1 wherein said antenna'unit is linear and extends vertically, said plates extend horizontally, and the portion of said line surrounded by said plates extends vertically.

6. An antenna system comprising a vertically elongated antenna unit,` a transmission line comprising two inner conductors surrounded by a shield and having the. inner conductors coupled at one end to said-unit, means insulating said antenna unit from said shield, and a plurality of spaced, parallel non-resonant metallic plates each having an opening therein through which said line extends, said plates being substantially horizontal While the portion of said line surrounded by said plates is substantially vertical,

said plates being positioned adjacent the unit and conductively connected to each other adjacent said openings and to the shield of the line, said line having a portion thereof substantially horizontally disposed at such a distance from said plates that at said plates the eld producedv by voltages in said horizontal portion will be approximately at right angles to the plates.

7. An antenna array comprising a pair of vertically-disposed elongated antenna units, a transmission'line including a pair of inner conductors, a shield about said conductors, said transmission line; coupling said units and having substantially the form of a vertically, disposed U, means` coupling said inner conductors at the ends of said line to said unitsl and the intermediate approximately-horizontal portion of said line spaced a given distance from said ends, means insulating said antenna units from said shield,

and a .pair of sets of spaced non-resonant mee,

, 5 tallic plates, each set surrounding one end of said line, the plates of each set being connected to each other and to the shield of said line.

8. An antenna array according to claim' 7 wherein said plates are parallel and extend horizontally, and said given distance is such that at said plates the field produced by voltages in said horizontal portion will be approximately at right angles to the plates.v

FRANK O. CHESUS. FRANK G. THOMAS.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date Bailey Dec. 2 6, 1939 Von Baeyer Sept. 29, 1942 Byrne Mar. 9, 1943 Kohl Jan. 4, 1944 Vogel June 20, 1944 Busgnies Aug. 5, 1947 Brown Dec. 7, 1948 

